Category Archives: Science

The word “vast” gets tossed around a lot to describe things like the backseat of an SUV, or a big lawn or the open ocean. These things can all be vast, depending on your frame of reference, but if there is anything that can truly be described as “vast” it is the universe.

The size of the universe defies any adequate description or human comprehension. Consider light. Light travels at the cosmic speed limit of 186,000 miles per second.

Satellite view of Chicago

I live in Chicago, and I am often amazed at how big this city is. I could spend my whole life exploring this city and not get to see everything. Google tells me that there are 4300 miles of road in Chicago — longer than the United States is wide — but light could travel every road in the entire city 43 times in one second. One second to travel the entire distance that my first car traveled in its entire lifetime. One second to travel around the Earth’s equator seven times.

Our sun is 93 million miles from where I am sitting. At a steady pace of 3 miles per hour, it would take 3500 years to walk to the sun without any breaks for eating or sleeping. The same light that can circle the whole earth seven times in one second takes 8 whole minutes to get from the sun to our planet. Along the way, there are two planets, one about the same size as earth, and one a bit smaller. Venus has a surface area of 177 million square miles — that’s over 750,000 Chicagos. There are six more planets in our solar system, a handful of dwarf planets, an asteroid belt, an Oort cloud, and more.

The nearest star to our own is Proxima Centauri. Light from our sun takes 4.3 years to get there. 4.3 years going as fast as it is possible for anything to travel.

Our planet is located in a backwater arm of the Milky Way Galaxy. Light takes 100,000 years to travel its diameter. The same light in the same time could circle the earth over 20,000,000,000,000 (20 trillion) times.

The nearest galaxy to the Milky Way is the Andromeda Galaxy. It is 220,000 light years across, and 2.5 million light years from Earth. Although it contains somewhere in the order of one trillion stars, the entire galaxy is only visible from Earth as a single point of light.

The observable universe is 93,000,000,000 (93 billion) light years across. Light would take 93 billion years to go from one end of the universe that we know to the other. There is more universe out there, but the light from those parts hasn’t reached us yet because the universe isn’t old enough. The universe is only 13 billion years old.

The observable universe is estimated to have around 100-200 billion galaxies. We don’t know exactly how many there are, because it would take too long for our instruments to count them all. And again, there is more to the universe than what we can see. We don’t know how much more because, well, we can’t see it.

The Hubble “Ultra Deep Field” is a view of part of the universe when it was less than a billion years old.

I hope I have given a glimpse of just how big the universe is. It is impossible for me to say exactly how big it is, not just because nobody knows, but because the size is completely incomprehensible. It defies language to describe it, and our brains to understand it. Even if the exact size were known, the number expressing it would be meaningless.

A lot of people hear how big the universe is and it makes them feel small. We are the center of our own lives, and what goes on in our lives is important to us. People used to believe that the Earth was the center of the universe because they couldn’t get their heads around the fact that we are unimportant. But to the universe, we are less than unimportant. For the sake of comparison, a speck of dust is in the order of 100µm (100 nanometers) wide. I am a little shy of 2 meters tall. I am therefore approximately 20 million times the size of a speck of dust (length, not volume).

The Earth has a diameter of about 12,000 miles. Our galaxy has a diameter of about 600,000,000,000,000,000 (600 quadrillion) miles. Our galaxy alone is 50 trillion times bigger than the Earth. People like to give “a speck of dust” as a measure of insignificance, but to our galaxy alone, the earth is far, far less significant than a speck of dust is to a human. And to the universe, our entire galaxy is insignificant. It is perfectly understandable that the universe makes some people feel small.

The size of the universe bothers me, too, but not because it makes me feel small. It has never been a problem for me to reconcile my own insignificance in the scheme of things.

I am troubled by the fact that I will spend my life exploring Chicago. I will spend my life getting to know one or two dozen people really well, a have a passing familiarity with maybe one or two hundred more. If I were still a researcher, I would spend my life trying to discover as much about the world as I could. As a non-researcher, I will spend my life learning as much of what others have discovered as I can. But there is so much that I will never know.

For all of the things we know about earth, there is so much more that we don’t know. We are just now starting to discover how common other planets are in our galaxy.

We know that the universe is believed to be about one quarter dark matter, but we don’t even know what dark matter is.

When I look up in the sky and see all that I can see, and understand what I can’t see, it makes me sad that I will never get to know so much of what is out there. So many galaxies. So many stars. So many planets. And I have to spend my life on just this one, with only my short life to see what I can see. There is so much to see on Earth, but the universe holds sights that we cannot possibly fathom.

The “Pillars of Creation”

I am troubled because I am a scientist, and I am greedy. Scientists are driven by the knowledge of the things we do not yet know. We see a hole in our knowledge and we want to fill it in. We are humbled by the knowledge of what we do not yet know, and seeing the vastness of the universe can be crushing.

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The internet is abuzz with the recent publication of an article in Science which replicated 100 studies in psychology, but only found positive results for a third of them. A lot of people are freaking out over this — both scientists and lay people — and I sure wouldn’t want to be one of those scientists whose study couldn’t be successfully replicated. But for those people, it isn’t the end of the world. Most of them didn’t screw up or do anything fraudulent. This is just how science works. A lot of people have talked about what this means about the state of science, or the state of psychology, or the state of whatever else, and I don’t have much to add to this conversation. But this does make me think about a few things about science in general, and it is those things that I want to say a few words about.

1) The publication of a study is not the end of the conversation. I think the media is guilty of misleading people about this. The truth is that you don’t sell many newspapers with headlines like, “scientists discover that X may be true.” What I see instead are headlines like, “scientists prove X is true,” or, “study disproves theory about X.” This isn’t how scientists think about things. If you have never had the pleasure of being in the presence of scientists when they hear the results of a new paper, it is a wonderful thing. More often than not, they will try to find problems with it. Maybe the author conceptualized their problem in the wrong way. Maybe they didn’t think of a confounding variable in their experiment. Maybe their statistics were misapplied. Maybe their mathematical model didn’t describe reality. To the lay person, this might make scientists sound petty for trying to take away a colleague’s accomplishment, but this is just part of the process.

Replication is not what you do to show that scientists are terrible, it is just a part of the process. When a new study comes out, scientists often say, “This is really interesting, but I’d like to see more work done on it.” What they are calling for, is more studies to see whether the effect can be reproduced in a different way. This is replication and is the process.

A few years ago, one of my own studies was subjected to a replication by another research team. They believed that we had failed to take a particular variable into account, and may have made a type I error as a result. I will admit that I figuratively bit my nails when I heard that this study was coming out. Nobody wants their study to be wrong. But it happened to turn out that even with the new variable included in the analysis, our hypothesis was still supported. It could have gone the other way.

This is part of why science is great — it is self-correcting. If one scientist draws the wrong conclusion, either innocently or maliciously, other scientists will be there to fix it. A scientific publication is not the end of the conversation. It is the beginning. When a scientist publishes a paper, they are saying, “This is what we think is going on, and here is some evidence that we are right. What do you think?”

2) When making conclusions in science, there are two types of possible errors: Type I errors and Type II errors. Type I errors are when you conclude that something is true, but it is not. Maybe your study concludes that watering plants with Brawndo (it’s got what plants crave) makes them grow better, when in reality it does not — type I error. A type II error is when you conclude that something is not true, but in reality it is. Maybe you conclude that monkeys are not actually primates, when they really are — type II error. A lot of the conversation around this replication study is about how scientists might be making too many type I errors. This could be true, but it is not my purpose here to comment on that. But I will point out that when you make it harder to make a type I error, you necessarily make it easier to make a type II error. Conversely, when you make it harder to make a type II error, you make it easier to make a type I error. Both types of errors are still errors, and you don’t want to make either one.

Here’s how it works: In science, we often use p-values as a tool for figuring out what happened. When you analyze your data, the p-value measures how likely it is that whatever trend you found in the data is the result of random chance and not a relationship between your variables. a p-value of 1.0 means that there is a 100% chance that your data is random numbers, and a p-value of 0.0 means that it is impossible for random chance to create those numbers (in reality, p-values are never exactly 0.0 or 1.0, but somewhere in between). Scientists use a cutoff of 0.05 for drawing conclusions — that is, you cannot tell people that you made a discovery unless there is a 5% chance or less of your data being meaningless noise. If the chance is 6% or higher, you cannot make any claims. Ideally, most things you find with a p-value of 0.05 or less are true, and most things that you find with a p-value higher that 0.05 are not true. But sometimes you have a real effect with a p-value higher than 0.05, which leads you to think it’s false (type II error), and sometimes you have an effect that is not real with a p-value that is lower than 0.05, and you think it’s real (type I error). If you lower the cutoff value to, say, 0.01, you will get fewer false positives (type I errors), but more false negatives (type II errors). If you raise the cutoff value to 0.1, the opposite happens — type II errors become less common, but type I errors become more common.

3) Science is hard, and we don’t know all of the answers. When we take science classes in school, there is always a right answer. You know that the substance is supposed to turn blue when you add the right chemicals, and if it doesn’t, you know you made a mistake. When I was a teacher, I would frequently have students come to me with a test tube full of orange fluid and ask, “is this right?” I would resist a straight answer as much as I could, because the purpose of the experiment was not to teach them how to make the fluid change colors, but to think like a scientist. The domain of scientists is the edge of human knowledge. There is no one to whom a scientist can ask, “is this right?” Because if there was, they wouldn’t be doing science. No one knows the answers to the questions that scientists ask, which is why scientists are trying to figure out the answers to those questions. This means that we will sometimes get it wrong. It is for this reason that I praise the scientists who do replication studies, as well as the scientists who did the original research. It is all part of the process.

Have a topic you want me to cover? Let me know in the comments or on twitter @cgeppig

Identical twins share all of their genes, but do not necessarily share identical environments. Image from wikimedia.org. Photograph by Christopher Michel

Nature or nurture? This is a question that is commonly asked by journalists and lay people. This seems like a reasonable question. There was a period of time when scientists asked it, too, but this time is over.

In modern biology, all traits are understood to be the result of the interaction between genes and environment. This goes for both physical and psychological traits.

But not all traits are equally the result of genes and environment. Some things are caused almost entirely by genes, with little input from the environment, and some are the opposite, with environment being almost entirely responsible for the trait. In one way or another, however, all traits require both. Biologists talk about this in terms of “heritability.” Heritability is a measure of the extent to which differences within a trait across individuals is the result of differences in genes across those individuals. It is expressed as a number between 0 and 1, where 0 is completely caused by the environment, and 1 is completely caused by genes. As a decimal, heritability can easily be converted into a percentage, which is a little easier to conceptualize. A heritability of 0.8 means that 80% of the variation in the trait across individuals is the result of genes. A heritability of 0.2 means that 20% of the variation is caused by genes. Here are some examples:

Consider height. It is unremarkable to observe that tall parents are likely to have tall children, and short parents are likely to have short children. I know a couple who are both over 6’1”, and their child is in the 95th percentile for height. But height has a heritability of only about 0.5. If you look at the variation of height across many people, only about half of that variation is due to genes, and the rest is due to environment. Tall parents can have short children if those children don’t get enough to eat, don’t get the right nutrients, or are exposed to a lot of infectious disease. Likewise, short parents can have tall children if the children grew up in a better environment than the parents.

Type II diabetes has a heritability of about 0.7, if you develop it before age 65. Genes play a big role in how likely you are to develop type II diabetes, and the rest depends on how much sugar and trans fat you eat. As they say, genes can load the gun, and environment can pull the trigger.

Estimates of the heritability of IQ range form around 0.2 to 0.8, although some recent studies have suggested that it is closer to the 0.8 end. Just as with height, IQ can be negatively affected by nutrition and infection.

The leading theory of personality claims that there are five dimensions to personality: agreeableness, openness to experience, extraversion, emotional stability, and conscientiousness. The heritability of these five dimensions ranges from around 0.4 to 0.6.

These traits that I list above all have fairly middling amounts of heritability, but there are also traits that are higher or lower. Eye color has a heritability of 0.8. The haircut you have right now has a heritability of close to zero, but it is probably not exactly zero.

Heritability calculations come mostly from twin studies. I won’t bore you with the computational details, but if you look at how likely identical twins are to share a trait vs how likely fraternal twins are to share the trait, you can get a pretty good idea of the genetic contribution to that trait. Identical twins share 100% of their DNA, meaning that all differences between them must come from environment.

There are also other things that go beyond just heritability. Even traits that have no direct genetic contribution rely heavily on genes. Take playing baseball, for example. Modern baseball has only been around for a couple hundred years — not enough time for evolution to have any impact on it. But playing baseball still relies on both genes and environment. Most obviously, playing baseball requires having been taught how to play the game — there is no genetic component to this. Any human of typical ability can be taught to play baseball. In addition to this, there are many traits with a clear genetic influence that are essential to playing baseball. A person must have a certain level of eye-hand coordination, interest in competition, and approximately two arms, two legs and two eyes. Certain musculature is required to be able to swing a bat and run. Cognition is required to understand the rules, and memory is required to remember them. All of these traits have genetic components. As a rather extreme example, a dog cannot play baseball. They lack the range of motion in their arms, the ability to stand easily on their hind legs, and hands that can grip a bat. Even if you tried to teach a dog to play baseball (environment) it would be unable to because of its anatomy (genes). On the other side, a perfectly functioning human is extremely unlikely to spontaneously begin playing baseball with no exposure to the game.

There are no traits that are entirely due to genes or entirely due to environment, making the “nature or nurture” question the wrong question.

Have a topic you want me to cover? Let me know in the comments or on twitter @CGEppig.

I have an opinion that might be unpopular around here: I don’t like music about science. My love of science and scientific knowledge cannot be impugned — my Ph.D. is all the evidence I need to make my case. I never would have made it through my 14 years of biology education if I didn’t love science. I even love boring science lecture — both hearing them and giving them. Music is also very important to me. I have been a casual musician for most of my life, and listening to music and making music are deeply fulfilling for me. There is a bunch of music out there that is about science, and it would be reasonable to guess that I would love this music. But I don’t. There is a time for music, and there is a time for a boring science lecture, but when I’m listening to music, what I want is not a boring science lecture.

Exhibit A:

Symphony of science is pretty popular. But let’s face it — this is literally just a boring science lecture that has been auto-tuned. The words of Carl Sagan, for example, are inspiring in their own right. I don’t think making them musical adds anything to them. If anything, I think his words are cheapened slightly by the gimmick.

Exhibit B:

I have a lot of love for Baba Brinkman, so I feel a little bit bad for listing him here. He is brilliant, great with words, and a good performer. I respect him a lot for using his medium to explain science. I particularly like the way he used this anti-evolution rally song as a base for this song about the science of political values and religion.

I got to see him perform once at an evolutionary psychology conference, and I really have nothing but love for him. For the times that I actually do want to listen to a boring science lecture set to music, I go straight to Baba Brinkman. But this doesn’t change the fact that his work is still essentially a boring science lecture, albeit spoken very rhythmically.

Exhibit C:

Hank Green’s “I Fucking Love Science” is cute. There are some clever lines, but it’s not what I want out of music. It is literal and a little bit lecture-ey at times. What I mean should be clear in a minute.

Please don’t misunderstand me — there is no judgement here. Musicians should write about whatever they want to write about, and people should listen to whatever they want to listen to. My feelings about the music I mention are just my own feelings. I also don’t mean to disparage any of these artists. I’ve tried writing music myself, and I can’t go around calling the kettle black.

This is not about what music I think people should or shouldn’t be writing and listening to, it’s just about what I want out of music. What do I want out of music? Some poetry. Some metaphor. The language of emotion. And would a drum solo kill you?

When I listen to music, I want to be able to identify with the emotions that are conveyed through the medium.

Take this song:

This song is reportedly about Kurt Cobain’s relationship with Tobi Vail, the drummer for Bikini Kill. You may not like this song as much as I do, but you will agree that at no point does this song, which is about a human relationship, sound like an anthropologist talking about the mating behavior of gorillas. The song is about the emotions, not the details. No boring lectures anywhere.

Kurt Cobain talks about his experience in this song without making the context perfectly clear. But it is deeply expressive and poetic, and it is exactly what I want out of a song.

Take another song about a relationship that ended:

Kris Kristofferson’s take on this topic has much more of a narrative style than Kurt Cobain’s. There is no question about what Me and Bobby McGee is about. But there is still poetry. He could have said, “Now she’s gone and I really miss her.” That would have communicated his point effectively, but there is no poetry to it. Instead, he chose to say, “and I’d trade all my tomorrows for one single yesterday.” Give me a minute to catch my breath.

I think the mistake that people make when writing music about science is talking like scientists instead of lyricists. There is a reason why we have scientists write our science, and musicians write our music. It has famously been said that, “Writing about music is like dancing about architecture.” Each of these media have their style, and limits to their application.

Here is what I would like to see: music about the experience of science, rather than the outcome of science. We have beautiful, poetic music about the experience of love, death, happiness, sex, jealousy, war, fatherhood, dissatisfaction, and basically every other human experience one could have. But very little beautiful, poetic music about science.

Consider, for a moment, Leonardo DaVinci. He was both a great scientist and a great artist. Remember that this was the guy who painted the Last Supper, the Mona Lisa, and the Vitruvian Man. If he was going to write a song about science, what would it have sounded like? “If the air passing over the top of a wing is moving faster than the air moving under the wing, it will reduce the pressure above the wing and create lift. La dee dee, la dee dah.” No, probably not.

Through my pursuit of science, I have experienced a wide range of emotions. Scientific discovery can be wonderful, beautiful, painful, emotional, and, at times, even exciting. Where is the music inspired by science that conveys these feelings?

You may disagree, or maybe I just haven’t heard the right music. What’s your favorite song about science?

Have a topic you want me to cover? Let me know in the comments or on twitter @cgeppig

The Man Behind the Curtain turns 1 today! In the past year, this blog has had over 4800 views from people in 104 nations. This surpassed what expectations I had, and I am looking forward to another good year.

America was settled by puritans. It may or may not be a coincidence that, hundreds of years later, we are still pretty weird about sex. Most people don’t even like saying the word “sex.” Enter “gender.” With the word “gender,” people can communicate their thoughts without the ickiness of having to say “sex” out loud. Or can they?

As a teacher, I often had to correct students who tried to tell me the gender of the cockroaches they were using in their experiments. Even biology professors, who really should have known better, would sometimes use the word “gender” when they meant “sex.” A friend of mine is having a baby soon. She and her husband recently made a big announcement about the gender of the baby. Official documents are notorious for items like, “Please indicate your gender: __male __female.” But what is the problem here? In short, sex and gender are not the same thing.

Sex is the biological component. Male mammals* have an X chromosome and a Y chromosome, have testicles, a penis, and produce sperm. Female mammals have two X chromosomes, have ovaries, a uterus, a vagina, and produce eggs. Sex is basically a categorical variable — you are either male or female. About 1% of people are “intersex.” For these people, there may be a disconnect between their arrangement of chromosomes and their anatomy — sometimes people will develop outwardly as male, but have two X chromosomes and no Y. The opposite can happen, too, with people developing outwardly as female, but having XY chromosomes. (People with XXY or YYX chromosomes are not considered intersex.) Sometimes people are born with ambiguous genitalia, or a mismatch between their external and internal genitalia. This throws a bit of a wrench into our concept of biological sex, but around 99% of people can be categorized comfortably as male or female. (For more information, go here.)

Gender is a psychological component. It deals with how you feel and how you present yourself. Unlike sex, which is mostly binary, gender is a smooth, continuous variable. Most human males are clustered towards the masculine end of the gender continuum, and most human females are clustered towards the feminine end of the gender continuum. But you can have males who are more or less masculine than other males, and females who are more or less feminine than other females. You can have females who are more masculine than some or most males, and males who are more or less feminine than most females. Most males identify as men, and most females identify as women, but this is not always the case. Some males identify as women, and some females identify as men — these people usually identify as “trans*” or “transgender.” (For more information, go here.)

So do cockroaches have gender? Not if the answer you are looking for is “male” or “female.” Male and female are choices for sex. Do cockroaches have a gender identity? Not as far as we know. Do cockroaches have any sense of self at all? Again, not as far as we know. There might be some scientific questions about cockroach gender, but most people don’t think about these things.